Wide-gap filler material

ABSTRACT

This invention relates to a composition for repairing metallic articles which in its initial state is in the form of an adhesive, self-supporting putty, capable of being molded including 5-15% by weight of a sacrificial binder containing at least one acrylic resin and volatile solvent. The invention also relates to a kit for the composition and methods for repair.

FIELD OF THE INVENTION

This invention relates to the brazing or sintering of particulatematerials and, more specifically, to the materials used for wide-gapjoining, repair or surface coating of gas turbine components.

BACKGROUND OF THE INVENTION

Gas turbine components, such as superalloy blades and vanes, aresubjected to high temperatures and stresses during engine operation.Under such conditions they will often become physically damaged due tothe formation of cracks, voids and worn surfaces. When the damageextends beyond certain allowable limits, a decision must be made toeither repair or replace the components. Because they are expensive tomanufacture, there is considerable economic incentive to attempt repairof turbine components by methods such as welding, brazing or wide-gapbrazing.

Wide-gap brazing refers to the repair of defects too large to be filledor bridged by standard brazing techniques wherein the gap fillermaterial is drawn into defects by capillary forces alone. Therefore,wide-gap filler materials must to be physically pre-placed within jointsor defects or onto surfaces and, during heat treatment, exhibit sluggishflow which prevents them from substantially flowing out of the repairarea. Prior art wide-gap filler compositions are typically comprised ofa mixture of superalloy and braze alloy powders suspended in some typeof temporary organic vehicle so as to form a slurry, paste or transfertape. The organic vehicle, or binder, is usually comprised of an organicpolymer dissolved in a solvent, and sometimes includes a plasticizer anddispersant. The organic polymer provides strength to the alloy powderdeposit after the solvent has evaporated, bonding the powder particlesto each other, as well as to the substrate article. (The word “binder”is usually used to mean all of the ingredients present in the vehicle,including the organic polymer, solvent, plasticizer, wetting agent, etc.However, in many references, the word “binder” refers specifically tothe organic polymer constituent of the vehicle. When used herein, theword “binder” shall be used in the traditional sense and the phrase“principle binder resin” shall be used to refer to the organic polymercomponent.) Subsequent drying and furnace heat treatment operationsdecompose and vaporize the various binder constituents, followed bybrazing or sintering of the powder. Alloy powders used for wide gapfiller materials are described in U.S. Pat. Nos. 4,073,639 and4,381,944. Organic binders and methods used in the formulation ofslurries, pastes and transfer tapes have been described in U.S. Pat.Nos. 2,908,072; 3,293,072 and 3,589,952.

Historically, wide-gap repairs were developed for the repair of defectsin aero or aero-derivative gas turbine components. Relatively speaking,these components and the defects in them tend to be small. For example,a typical wide-gap crack in an aero gas turbine component might be about1/14 inch-in length by about 0.030 inches in width or depth. Incontrast, heavy frame gas turbines which are designed primarily forindustrial power generation are much larger than aero or aeroderivativegas turbines. A single vane segment or blade from one of these enginescan weigh upwards of 100 lbs. Crack defects in these components arecorrespondingly much larger, with dimensions often exceeding severalinches in length and up to one inch in width or depth.

Standard welding techniques cannot always be used to successfully repairthis type of damage, and it is again desirable to be able to use sometype of wide-gap repair process for component restoration.

While the wide-gap slurries, pastes and transfer tapes of the prior arthave been found useful for the repair or joining of the smaller areocomponents, there are many situations in which these materials areunsatisfactory for the repair of larger defects in heavy frame gasturbine components. For instance, it is often desirable to be able toapply the wide-gap filler material to thicknesses of ⅛ inch or more ontosurfaces with vertical or inverted orientations. After it is applied,the filler material should neither flow, shrink, nor form defects suchas voids, tears and the like during subsequent handling and heattreatments. Prior art wide-gap repair materials will either slump orfall off the article during drying and/or heat treatment when used inthis way, making it necessary to complete the brazing or liquid phasesintering operation in a number of steps by varying the orientation ofthe article in the furnace each time.

Some additional requirements of a good wide-gap filler material arethat, during its initial application, it should be capable of plasticflow together with adhesive properties which are similar to those of amodeling clay. These properties would allow the alloy powder mixture toflow into a desired shape by applying a moderate force, for example byhand, and thereafter keep its shape, while adhering to the substratearticle in various orientations. Once the external force is removed fromthe wide-gap filler, it should keep its shape while the repair articleis handled, stored, dried, and heat treated. These attributes are notfound in the wide-gap slurries, pastes and transfer tapes of the priorart. For example, a powder metallurgy repair material, comprised of amixture of iron-base alloy powders and a plastic binder, has beendescribed in connection with the repair of centrifugal pump impellers(Welding Journal, April 1971, pp. 255-256). The proprietary materialsused in this method were molded by hand, however, back-up supports wereneeded on the underside of through-going defects to hold the powder mixin place. In other words, the mixture was not self-supporting.

Still another limitation of prior art wide-gap filler materials has beenencountered in the repair of hollow gas turbine components which containthrough-going defects or details. In most cases, drop-through or flow ofthe repair filler material into interior cooling passages or cavitiescannot be tolerated, since obstruction of these passages would renderthe component unserviceable and unrepairable due to the limited accessafforded by the component design. It is very difficult to control theflow of prior art wide-gap pastes and slurries which makes them unsuitedto the repair of these types of defects or details. An importantadvantage of the wide-gap filler material of the present invention isthat the aforementioned limitations related to molding, flow, slumpingand loss of adhesion can be eliminated. This advantage is realizedthrough the use of the novel sacrificial binder system of the presentinvention.

Finally, within the general category of materials comprised of metalpowder alloys and organic binders there exists another class ofmaterials which are used in the powder injection molding art. Powderinjection molding (herein, referred to as PIM) is a method for thefabrication of ceramic or metallic sintered parts. A solid green body orcompact comprised of a ceramic or metallic particulate material and asacrificial binder mixture is molded in a die by the application of heatand mechanical pressure in an injection molding machine. The binderingredients are later removed from the green body in a series of solventor thermal debinding processes, followed by firing and sintering of thecompact. The main PIM binder types are thermoplastic, thermosetting andgelation systems (R. M. German, Powder Injection Molding, Metal PowderIndustries Federation, Princeton, N.J., 1990, pp. 99-124). Thermoplasticsacrificial binders used in the formulation of PIM feedstock are rigidand non-adhesive at room temperature and must be softened by heatingbefore the mixture will flow adequately to allow mold fixing.Thermosetting and water-based gelation binders develop their strength bycross-linking of the polymer units at elevated temperatures. Rigid,self-supporting compacts can only be produced from these materials byheating the die cavity after the feedstock has been introduced. The needfor substantial temperature and pressure variations during theprocessing of PIM feedstocks makes the binders used in theseformulations unsuitable for use in conjunction with the wide-gap fillermaterials of the present invention.

SUMMARY OF THE INVENTION

One object of the present invention is to provide an improved wide-gapfiller material, useful for the manufacturing, joining or repair ofmetallic articles which will allow the positioning and heat treatment ofthick (e.g. ⅛ inch), complex, near-net-shape powder alloy deposits inhorizontal, vertical or inverted orientations without the need forsurrounding back-up dams or support materials.

Another object is to provide a wide-gap filler material which, in itsinitial form, will remain soft, moldable, self-supporting and adhesive(tacky), even after being exposed to air at room temperature over aperiod of several hours.

Still another object is to provide a wide-gap filler material which willnot slump, shrink, crack or flow away from its initial position duringsubsequent handling or vacuum heat treatment operations, even when it ispositioned in vertical or inverted orientations.

A further object is to provide a wide-gap filler material which can beused to fill through-going defects in hollow components where there islimited or no access to the interior cavity. The improved wide-gapfiller material of the present invention will not slump or drop throughinto the interior cavities of the component during application orprocessing.

These and other objects and advantages will be more fully understoodfrom the following detailed description of the preferred embodiments,which are intended to be typical of, rather than in any way limiting on,the scope of the present invention.

Briefly, in one form of the present invention there is provided animproved sacrificial binder mixture consisting essentially of, byweight, 31-33% acrylic resin, having a glass transition temperature(T_(g)) less than 20° C., 22-24% phthalate or adipate-type plasticizer,42-44% glycol ether or glycol ether acetate with a vapor pressure ofless than 20 mm Hg. at 25° C. and 1-2% nonyl phenol base or octyl phenolbase nonionic surfactant as a wetting agent. The binder mixture iscombined with a finely divided alloy powder or blend of powders to givea composition consisting of, by weight, 5-8% of the binder mixture and92-95% of the alloy powder or powders. The resulting filler material isin the form of an adhesive, self-supporting, moldable putty, capable ofbeing forced under manually applied pressure to bond with and take theshape of, a joint or repair cavity in any orientation.

In another form of the present invention, there is provided a two-part(Part A and Part B) wide-gap filler material comprised of two powderedalloys, provided as separate components, each in the form of a moldable,adhesive putty. The first component (Part A) putty comprises a metalalloy powder having as its basis metal an element selected from thegroup consisting of nickel, cobalt or iron. The first component puttymay, in addition, contain a certain amount of a non-metallic (e.g.oxide, nitride or carbide) particulate material. The second metallicalloy powder has a liquidus temperature lower than the solidustemperature of the first component particulate material(s) and thesubstrate article. The ratio of these two putty components, Part A(containing the first alloy powder(s) plus binder mixture): Part B(containing the second alloy powder plus binder mixture), is controlledto be in the range from 4:1 to 1:1, depending on the properties requiredin the final repair deposit and the processing characteristics of thealloy powders when they are used to repair or join the metal articles.

The invention in still another form provides a method for using theputty containing the improved sacrificial binder of the presentinvention to manufacture or repair a metallic article. After preparationand cleaning of the bonding or mating surfaces, a single or two-partalloy putty is applied to the article and shaped or molded to produce anear-net-shape build-up. The sacrificial binder ingredients are thenremoved in a controlled thermal process to prevent flow, slumping, orseparation of the repair deposits from the article. The sacrificialbinder ingredients are additionally removed by methods which allowvapors and gaseous decomposition products to escape from the wide-gapfiller material without causing internal pressure build-ups which couldotherwise lead to the formation of defects such as voids, blisters,cracks, tears and the like.

This application also relates to a kit for the composition and methodfor repair.

DESCRIPTION OF A PREFERRED EMBODIMENT

In the repair or joining of metallic articles using wide-gap fillermaterials in accordance with the present invention, defects within wornarticles are first removed by mechanical means or the surfaces of thejoint are brought into position with one another. A particulate filleralloy is blended with a sacrificial binder to form the wide-gap fillerand is then placed within the repair cavity or between the jointsurfaces. Portions of the sacrificial binder are removed by drying thearticle in air at temperatures up to 200° C. and then the article isplaced into a vacuum furnace to be brazed or liquid phase sintered.During the overall brazing or liquid phase sintering process, thearticle is first held at an intermediate temperature which causes theremainder of the sacrificial binder ingredients to decompose intogaseous products and be removed by evaporation. The temperature is thenraised to a point at which the wide-gap material melts, re-solidifiesand fuses with the parent metal of the article forming a sound, highstrength joint.

The sacrificial binder system of the present invention comprises atleast a principle binder resin which is a thermoplastic and has asoftening or glass transition temperature (T_(g)) below about 20° C.,and a solvent with a low vapor pressure, preferably less than about 20mm Hg at 25 C. Additionally, the sacrificial binder system of thepresent invention may contain a plasticiser and a wetting agent. The lowglass transition temperature of the principle binder resin makes it softand malleable at room temperature, while the low vaporization rate ofthe solvent contributes to wet tack, adhesion and a useful working life.When combined with alloy powders, these binder properties result in awide-gap filler material with a consistency somewhat like modelling clayor adhesive putty.

The principle binder resin preferably comprises an acrylic polymer orblend of acrylic polymers which provide a balance of cohesive strengthor rigidity and softness or flexibility. For example, a tough, hardresin which has good strength and a high softening temperature can beplasticized with a softer, more flexible resin to give the desiredproperties. If the glass transition temperature of the principle binderresin is low enough, it may even have a slight tacky feel even beforesolvents and plasticizers are added. Acrylic resins have other desirableproperties which make them useful as ingredients in the sacrificialbinder system of the present invention. For example, acrylic resinsremain stable above their softening range at temperatures up to 170-230°C. This property allows the selective removal of the solvent portion ofthe binder to take place by evaporation in air at temperatures up to150° C., prior to vacuum furnace heat treatment. At higher temperatures(i.e. above 260° C., acrylics depolymerize to volatile monomers, leavingnegligible ash or solid residue in the repair deposits. Some examples ofacrylic resins which are used in conjunction with the present inventionare methacrylate, methyl methacrylate, ethyl methacrylate, n-butylmethacrylate, isobutyl methacrylate, methyl/n-butyl methacrylate,n-butyl/isobutyl methacrylate, methyl/laurel methacrylate polymers andcopolymers. It is preferred that the principle binder resin make up25-50% by weight of the sacrificial binder system and most preferably30-40% of the sacrificial binder system.

The solvent used in conjunction with the sacrificial binder of thepresent invention must be active, which is to say that it is capable ofdissolving the principle binder resin. Initially, the solventcontributes to the wet tackiness, softness, and moldability of thesacrificial binder system. After the wide-gap filler material has beenapplied to an article to be repaired or joined, the principle binderresin is dried and hardened by evaporation of the solvent. Thus, thesolvent must have a low volatility at room temperature in order toprovide a useful working life (e.g. several hours) once it is exposed tothe atmosphere, but substantially vaporize when heated to temperaturesup to 200° C. When used in conjunction with the sacrificial binder ofthe present invention, it is desirable that the solvent have a vaporpressure below 20 mm Hg at ambient temperature and most preferable thatthe vapor pressure be below 1 mm Hg at ambient temperature. The solventmust vaporize completely and cleanly during air drying and vacuumfurnace burnout. Additionally, it is desirable that the solvent pose alow health risk during handling and drying. Solvents which arecompatible with the sacrificial binder system of the present inventionare esters such as isoamyl acetate and isobutyl acetate, hydrocarbons,such as VM&P naptha and mineral spirits and glycol ethers and acetatessuch as propylene glycol methyl ether, dipropylene glycol methyl ether,tripropylene glycol methyl ether, propylene glycol methyl ether acetateand dipropylene glycol methyl ether acetate. The glycol ethers andacetates and hydrocarbons are most preferred in the present inventionsince they pose the lowest health risks and meet the most preferredvolatility criteria listed above. It is preferred that the solvent makeup 25-60% by weight and most preferably 30-45% of the sacrificial bindersystem.

In addition to the principle binder resin and solvent, the sacrificialbinder system of the present invention may optionally contain aplasticizer. The plasticizer further lowers the softening temperature ofthe principle binder resin and provides added flexibility, softness andadhesion. The plasticizer must be chemically compatible (i.e. formsolutions) with the principle binder resin and solvent, sufficientlyvolatile to allow its removal during the vacuum furnace binder burn-outprocess, but not sufficiently volatile to be substantially removedduring mixing, storage, molding or air drying. The plasticizer mustfurther completely decompose into gaseous, volatile species at hightemperatures without leaving substantial level of solid residue.Plasticizers which have been found to be useful in the present inventionand which have the above desirable properties include phthalic andadipic esters. Some examples of phthalic esters which can be used toplasticize the acrylic principle binder resins are alkyl benzylphthalate, butyl benzyl phthalate, butyl octyl phthalate, dibutylphthalate, dicyclohexyl phthalate, diethylphthalate, dihexyl phthalate,diisodecyl phthalate, di-2-methoxyethyl phthalate, dimethyl phthalate,ditridecyl phthalate, di-2-ethylhexyl phthalate, diisooctyl and mixedoctyl phthalate, n-octyl n-decyl phthalate and isooctyl isodecylphthalate. Some examples of adipic esters which can be used toplasticize acrylic resins are dioctyl adipate, diisodecyl adipate,di-2-ethylhexyl adipate. octyl decyl adipate, diisobutyl adipate anddiisooctyl adipate. It is preferred that the plasticizer make up 0-30%by weight and most preferably 15-25% of the sacrificial binder system.

Finally, the sacrificial binder resin of the present invention may,optionally, contain a wetting agent. The wetting agent lowers thesurface tension of the binder system, promoting adhesion to the repaircavity or joint surfaces and dispersion of powder particles. The wettingagent must also be compatible with the other binder ingredients and burnout cleanly from the filler material leaving negligible ash or soliddeposits. Wetting agents which have been found to be useful inconjunction with the binder system of the present invention are nonyl oroctyl phenol base nonionic surfactants. Some examples of nonyl phenolbased surfactants are nonylphenol polyethylene glycol ether andnonylphenoxypolyethoxyethanol nonionic surfactant. An example of anoctyl phenol base surfactant is octylphenoxypolyethoxyethanol nonionicsurfactant. It is preferred that the wetting agent make up 0-5% byweight of the sacrificial binder system and most preferably 1-2% of thesacrificial binder system.

The metallic particulate filler alloy used in conjunction with thesacrificial binder of the present invention can be of any composition orblend of powders which may be required to produce satisfactory repairjoints, as required by the application. Spherical or at leastregularly-shaped particles are preferred since they form smoother, moreuniform putty mixtures. Irregular or agglomerated powder particlesrequire larger amounts of binder and do not form smooth, homogeneousmixtures. In a preferred form of the present- invention, the particulatematerial will pass through a −325 mesh standard sieve. Particles whichare substantially coarser than −325 mesh size result in putty mixtureswhich have a granular texture and do not flow as smoothly to fill repaircavities. A fine particle size also promotes sintering and solid-statebonding of the filler powder to adjacent surfaces during removal of thelast binder components in the vacuum furnace.

In preparing the moldable, self-supporting wide-gap filler materials ofthe present invention, it is essential that the ratio of the sacrificialbinder to the particulate alloy be controlled to produce the desiredproperties. If too little of the sacrificial binder is used, the repairfiller material will have a granular texture, lacking sufficientcohesive and adhesive strength to be properly shaped and molded. If anexcess of binder is used, a number of problems may be encounteredincluding slumping of the repair deposit during handling, drying or heattreatment due to particle settling and migration, distortion duringbinder removal and sintering, separation of the binder from theparticulate constituent, leading to nonhomogeneities in the appliedfiller material. The most preferred sacrificial binder/powdercomposition of the present invention corresponds to that in which thereis just enough binder present to fill the interstitial spaces betweenthe alloy powder particles. At this composition, which is known as thecritical loading point, the alloy powder particles are in an optimalpacking arrangement which results in point-to-point contact betweenadjacent particles. This is also the composition at which the puttyattains the highest viscosity and resistance to flow or deformation. Thecritical loading composition thus attains the greatest gravitational anddimensional stability, thereby preventing shrinkage and slumping of thefiller material after it is applied. The critical loading compositioncan be estimated using theoretical models which are based on thecharacteristics of the particulate material, but can also be identifiedusing simple tests derived from paint technology. Essentially, thesacrificial binder is added incrementally to the particulate materialand mixed by hand until the mixture looses its granular texture and canbe spatulated into a stiff, but coherent paste.

The preferred ratio of the sacrificial binder to particulate material inconjunction with the moldable wide-gap filler material of the presentinvention therefore corresponds to that of the critical loadingcomposition. Expressed in terms of weight percentages, the criticalloading composition typically corresponds to 5 to 8% of the binder ofthe present invention. Finally, it is noted that the optimal orpreferred loading compositions of prior art brazing slurries, pastes orfeedstocks used for powder injection molding are substantially differentthan the critical loading composition. The optimal compositions forthese latter materials correspond to the case where binder loadingexceeds the critical level in order to allow the powder particles tosettle and compact, as in the case of a slurry, extrude through asyringe, as in the case of a brazing paste, or flow into a die, as inthe case of powder injection molding.

In preparing the wide-gap filler materials of the present invention, ithas been found to be particularly advantageous to premix and dissolvethe sacrificial binder ingredients, followed by the addition and mixingof the particulate alloy. Premixing the binder ingredients results inrapid and complete dissolution of the principle binder resin, solvent,plasticizer and wetting agent. The latter process can be accomplishedusing a high speed (4,000 to 10,000 rpm) impeller mixer. Mixing anddispersion of the particulate material with the sacrificial binder ispreferably accomplished at slower speeds (25-70 rpm) in a vacuum shearmixer. Vacuum mixing is considered to be essential to prevent theentrapment of air within the filler material which could lead to voidsin the finished repair deposits.

After the sacrificial binder and powder have been thoroughly mixed andvacuum degassed, the resulting moldable wide-gap filler putty is readyto be discharged, packaged or used directly for repair or joiningpurposes. Due to the high viscosity of the putty it will not flow freelyand must be removed from the mixing container either by scraping with aspatula or by pump. Since manual scraping or scooping is laborious, timeconsuming and presents the risk of re-introducing air pockets into themixture, the preferred method of removing or discharging the putty fromthe mixer is by mechanical pump. For such highly viscous materials, aram/follower plate discharge system is required. In this process a flatplate is forced downwards into the vessel containing the mixed puttycompound using a hydraulic press. The putty flows out through an openingin top of the follower plate, from which it may be directly dispensedinto holding containers or packages until needed for productionpurposes. Alternatively, the putty being discharged from the followerplate can be directed to a transfer pump and/or a piston metering systemin those cases where repeatable, controlled amounts of the material areto be used, or where a controlled ratio of ingredients is required for aspecific purpose. When the material is to be applied in variablequantities, as would be typical of the case where the repair ofservice-exposed gas turbine components is to be accomplished, it ispreferred that the putty be provided on flat sheets or trays. Transferpumps and metering systems are more suited to higher volume, productionline assembly or fabrication operations.

In a preferred embodiment of the present invention, the moldablewide-gap filler material is provided in the form of a two-componentcompound, supplied and packaged as a kit with dual beads of putty in aholding tray, or dispensed directly from a dual barrel cartridge. Thefirst component (Part A) has a composition substantially equivalent tothat of the basis alloy of the article to be repaired or joined, whilethe second component (Part B) has a liquidus temperature below themelting range of the first component. Alternatively, the first alloy mayhave a composition different from the basis alloy of the article to berepaired in order to provide specific engineering qualities (i.e.strength, wear or abrasion resistance). This two-component material isintended for use in conjunction with the wide-gap powder metallurgyrepair method of U.S. Pat. No. 5,156,321. In this process, Part A of thewide-gap filler material is positioned within the repair area or jointand Part B is applied onto the surface of the Part A putty, followed byheating of the article to remove the sacrificial binder and to effectpartial solid state sintering and liquid phase sintering of theparticulate material. The volume ratio of the Part A and B components isadvantageously controlled by simultaneously dispensing side-by-sidebeads of the first and second component putties from a dual dischargecartridge with a fixed discharge ratio. If they are not to be usedimmediately, the dual beads may be stored in a temporary holding tray.During application of the repair material, this fixed ratio of A to B ismaintained by using equal lengths of the two putty beads. This methodeliminates the need to weigh or measure the volume of each repairdeposit as it is being applied to the component.

The moldable wide-gap filler material of the present invention can bemanually applied to irregular or complex-shapes using hand tools orsimply by applying finger pressure and working the putty into a repaircavity or joint. Care is taken to eliminate any voids or areas ofnon-contact between the filler and the joint surfaces which could leadto defects in the article after thermal processing. The surface of thewide-gap filler material is molded into a desirable near-net-shape whichsubstantially corresponds to the original surface contours of thearticle, thereby reducing the amount of time required to blend andfinish the surface of the joint after heat treatment.

After it is applied, the wide-gap filler material is dried in an airoven in order to remove the solvent component of the sacrificial binder.This process ultimately hardens the filler deposit and renders it porousso that the remainder of the binder system can be removed in asubsequent vacuum heat treatment operation without causing internalpressure build-up or defect formation due to entrapped vapors. Whenraising the temperature of the article in an air drying oven, it iscritical that the rate of heating and solvent removal be controlled toavoid distortion, slumping or the formation of gas porosity within theputty deposit. An exemplary drying cycle of the present inventioninvolves raising the temperature of the air drying oven to 75° C. at arate of 5 to 10° C. per minute. After holding at this temperature forfour hours, the temperature is raised at the same rate to 150° C. andheld for another four hours.

Once the filler deposits have been dried, the remainder of thesacrificial binder ingredients are removed by thermal decomposition andvaporization in a vacuum brazing or sintering furnace. Completevaporization and elimination of the last binder ingredients of thepresent invention usually occurs at temperatures below 500° C. Afterthis exposure, all solid organic residues are substantially eliminatedfrom the repair joint, leaving only the metallic alloy powder materialswhich are then melted and fused or sintered by further increases intemperature.

The binder of the present invention may also be used as an adhesive forthe placement and bonding of powder alloy tapes. In many repair ormanufacturing applications, it is a requirement that these tapes beapplied in vertical and inverted orientations. The braze paste bindersof the prior art have been used for this purpose but are not capable ofholding thick tape deposits in these orientations. The binder of thepresent invention can be applied by brushing or spray to the bondingsurface of the tape or substrate article and used as an effective glueto overcome these prior limitations.

In another embodiment, the particulate component of the wide-gap fillermaterial of the present invention may be a blend of alloy powderscomprised of a mixture of metallic powder and hard particles useful forcreating hard, wear or abrasion resistant layers. The hard particles maybe metal nitrides, oxides, carbides, borides, or mixtures thereof. Suchwear and abrasion resistant layers (hardfacing) can be applied to thesurface of cold-working or hot-working tools to extend their lifetimesin service. There are many applications for this type of hard coating inthe gas turbine field, on areas such as airfoil shroud faces, fuelnozzles, seal surfaces and the like.

The following examples are illustrative of the invention.

EXAMPLE 1

The combination of sacrificial binder ingredients shown in Table I weremixed together using a high speed impeller mixer for 5 minutes at 5000rpm. A filler alloy powder was then added to the binder ingredients andmixed for an additional 10 minutes at 2500 rpm. The mixture was thentransferred to shallow trays where the most volatile solvents (tolueneand methyl ethyl ketone) were allowed to evaporate for 48 hours. TABLE I% WGT Methacrylate Polymer 2.70 (T_(g) = 5° C., supplied as 40% solidsin toluene) Ethyl Methacrylate Copolymer 1.05 (T_(g) = 40° C., suppliedas 30% solids in methyl ethyl ketone) Butyl Benzyl Phthalate 1.02Dipropylene Glycol Methyl Ether Acetate 2.16Octylphenoxypolyethoxyethanol Nonionic Surfactant 0.07 Repair FillerAlloy Powder (−325 mesh) 93.00

The resulting filler compound was in the form of a moldable, adhesiveand self-supporting putty. This material was bonded to clean metalarticles in vertical and inverted orientations without visibly slumpingor separating after periods of up to 24 hours at room temperature.

EXAMPLE 2

The sacrificial binder ingredients shown in Table II were mixed togetherusing a high speed impeller mixer for 5 minutes. The filler alloy powderis then added to the binder ingredients and the resulting combination ismixed and vacuum degassed in a double planetary mixer at 1 Torr absolutepressure for an additional 10 minutes. TABLE II % WGT n-ButylMethacrylate Polymer (T_(g) = 15° C.) 2.18 Butyl Benzyl Phthalate 1.56Dipropylene Glycol Methyl Ether Acetate 2.92Octylphenoxypolyethoxyethanol Nonionic Surfactant 0.14 Filler AlloyPowder (−325 mesh) 93.2The resulting wide-gap putty had properties similar to those describedabove for the putty mixture of Example 1.

EXAMPLE 3

During an engine overhaul, a cobalt-based industrial gas turbine vanesegment, with a composition as given in Table III, was inspected andfound to contain numerous large cracks. The defects were of such sizeand location as to prevent them from being welded without the risk ofcreating additional cracks and distortions within the component. Thecracks were also present in various horizontal, vertical and invertedorientations. The defects were first mechanically removed by grinding,leaving surface discontinuities to be repaired. The vane segment wascleaned for four hours at 1150° C. under a partial pressure of hydrogen.A two-part repair filler material comprised of two powdered alloys wasprepared, with each part provided separately in the form of a moldable,adhesive putty. The first alloy powder (Part A) was aprecipitation-strengthened nickel-base superalloy. The second alloypowder (Part B) was also a nickel-based powder with a melting rangelower than the first alloy powder, due to the addition of boron as amelting point suppressant. The weight percent contents of the two alloypowder constituents are also given in Table III. Each of these twopowders was mixed separately with the sacrificial binder ingredients togive putty compositions as defined in Table II.

Part A filler putty was manually positioned and shaped to fill eachrepair cavity. Part B putty was applied on top of the Part A puttydeposit. The vane segment was dried in air for four hours at 75° C. andthen for an additional four hours at 150° C. The article was transferredto a vacuum heat treating furnace which was evacuated to an absolutepressure of less than 1×10⁴ Torr. The temperature was initially raisedto 250° C. over a period of about 30 minutes. Over the next 3 hours, thetemperature of the furnace was raised to 450° C. while outgassing of theremaining binder ingredients occurred. Over the next 5 hours thetemperature of the furnace was raised to 1204° C. and held for 2 hourswhich resulted in liquid phase sintering of the repair filler material.The article was then cooled to room temperature to yield the finalrepaired part. The sintered repair filler material was completely bondedto the metal article and did not show signs of shrinkage, separation orflow, even in areas where the deposits were in inverted and verticalorientations. The small amount of positive material on the surface ofthe defects was then manually blended away to restore the originalsurface contour of each repair area. TABLE III Part A Part BCobalt-Based Filler Alloy Braze Alloy Element Vane Alloy (−325 Mesh)(−325 Mesh) Ni 10.5 Balance Balance Cr 25.5 16.0 14.0 Co Balance 8.510.0 Al 3.5 3.5 Ti 3.5 W 7.5 2.6 Mo 1.75 Ta 1.75 2.5 Nb 0.85 C 0.25 0.10B 0.01 0.01 2.7 Zr 0.06 Y 0.06

EXAMPLE 4

The combination of sacrificial binder ingredients shown in Table IV aremixed together using a high speed impeller mixer for 5 minutes at 5000rpm. A filler alloy powder is then added to the binder ingredients andmixed for an additional 10 minutes at 2500 rpm. The mixture is thentransferred to shallow trays where the most volatile solvents (tolueneand methyl ethyl ketone) are allowed to evaporate for 48 hours. TABLE IV% WGT Methacrylate Polymer 3.25 (T_(g) = 5° C., supplied as 40% solidsin toluene) Ethyl Methacrylate Copolymer 1.05 (T_(g) = 40° C., suppliedas 30% solids in methyl ethyl ketone) Dipropylene Glycol Methyl EtherAcetate 2.16 Repair Filler Alloy Powder (−325 mesh) 93.59The resulting filler compound is in the form of a moldable, adhesive andself-supporting putty. This example demonstrates a sacrificial bindercomposition which excludes plasticizer and wetting agent. The low glasstransition temperature of the Methacrylate Polymer (which, together withthe Ethyl Methacrylate Copolymer, constitutes the principle binderresin) provides sufficient plasticity to make a moldable putty.

EXAMPLE 5

For comparison with the wide-gap filler material of the presentinvention, two wide-gap filler compositions were prepared which werecomprised of alloy powders mixed with commercially available braze pastebinders. The two commercial binders used for this purpose are well knownand widely used by those skilled in the brazing art. They are consideredto be typical of the two general classes of braze paste binderscurrently in use: (i) water-based gel binders containing polymersderived from natural cellulose and (ii) solvent-based binders containingsynthetic organic polymers (thermoplastics). In the first comparativewide-gap filler, a nickel-based alloy powder, with a compositionequivalent to that of the Part A Filler Powder in Table III, was mixedwith a commercial braze paste binder known as “KAO” (Omni TechnologiesCorporation, Exeter, N.H.). This binder is a water-based gel containingcellulose ether (approximately 3%) as the principle binder resin andthickener. The KAO binder was added to the alloy powder incrementally tothe point at which the mixture was no longer granular, but formed astiff, cohesive paste; the total amount of KAO being in the range of 4-6weight percent.

A second comparative wide gap filler material was prepared using thesame alloy powder and another commercial braze paste binder known asNicrobraz 500 Cement (Wall Colmonoy Corporation, Madison Heights,Mich.). This binder is comprised of a plastic (approximately 6 weightpercent) dissolved in an organic solvent (1-1-1 Trichloroethane). Awide-gap filler putty containing this binder was prepared in the sameway as for the KAO binder, using approximately 4-6% weight percent ofthe Nicrobraz 500 Cement.

For each of these two commecial braze paste binders, it is to be notedthat the amounts of the principle binder resins, cellulose ether andplastic, are much lower (3 and 6 weight percent, respectively) than inthe sacrificial binder of the present invention (25-50 weight percent),but as stated above, they are typical of those currently used in theart. In addition, the organic solvent used in the Nicrobraz 500 cement,1-1-1 trichloroethane, has a much higher vapour pressure. (approximately125 mm Hg at 25° C.) than the solvents preferred for use in thesacrificial binder of the present invention.

These two comparative wide-gap filler materials were found to beinferior to the wide-gap filler material of the present invention forthe following reasons:

-   1. They were both weak and did not have enough firmness or “body” to    be easily molded by hand into free standing shapes. On the contrary,    they each had a wet consistency and tended to pull appart easily    during handling. It was suspected that this was due to the low    levels of principle binder resin and high solvent levels in each of    the commercial binders. This weakness also made each of the    comparative wide-gap fillers prone to slumping and distortion during    handling.-   2. The comparative wide-gap filler materials would not adhere to    vertical and inverted surfaces. Once again, the low levels of    principle binder resin were thought to be responsible for the poor    performance.-   3. The comparative wide-gap filler materials each dried out too    quickly. Their surfaces became hard and brittle after 10 to 15    minutes of exposure to air, making them prone to tearing and    cracking when attempts were made to mold them into free-standing    shapes after this period of time had elapsed. This deficiency was    caused by the comparatively high vapour pressures and fast    evapouration rates of the solvents used in the commercial braze    paste binders.

EXAMPLE 6

A two-part, high-temperature hardfacing compound is formulated asfollows using the sacrificial binder ingredients of Example 2 and nickelchromium—chromium carbide composite powders whose mesh sizes are both−325 mesh. TABLE V % WGT Part A n-Butyl Methacrylate Polymer (T_(g) =15° C.) 4.91 Butyl Benzyl Phthalate 3.51 Dipropylene Glycol Methyl EtherAcetate 6.56 Octylphenoxypolyethoxyethanol 0.32 Nonionic SurfactantMetco 83 VF-NS Composite Powder, −325 Mesh 84.7 (50% chromium carbideclad with 50% nickel-chromium alloy) Part B n-Butyl Methacrylate Polymer(T_(g) = 15° C.) 2.18 Butyl Benzyl Phthalate 1.56 Dipropylene GlycolMethyl Ether Acetate 2.92 Octylphenoxypolyethoxyethanol 0.14 NonionicSurfactant Amdry XPT 476 Alloy Powder, −325 Mesh 93.2 (Ni—15Cr—3.5B)Each Part is in the form of a moldable, adhesive and self-supportingputty. The Part A putty is applied to the Z-notch (contact surface) of ashrouded industrial turbine blade. The Part B putty is applied to thesurface of the Part A putty to give an approximate weight ratio of60:40, Part A:Part B.

The composite powder deposits are dried in air for four hours at 75° C.and then for an additional four hours at 150° C. The blade istransferred to a vacuum heat treating furnace which is evacuated to anabsolute pressure of less than 1×10⁻⁴ Torr. The temperature is initiallyraised to 250° C. over a period of about 30 minutes. Over the next 3hours, the temperature of the furnace is raised to 450° C. whileoutgassing of the remaining binder ingredients occurred. Over the next 5hours the temperature of the furnace is raised to 1176° C. and held for30 minutes which results in liquid phase sintering of the compositewide-gap filler material. The article is then cooled to room temperatureto yield the final repaired part. The bonded composite powder providesthe interlocking Z-notch contact surfaces with enhanced wear resistancewhile the blades are operating in a gas turbine engine.

The present invention has been described in connection with specificexamples and embodiments. However, it will be understood by thoseskilled in the art that the invention is capable of other variations andmodifications without departing from its scope as represented by theappended claims. The above references are hereby incorporated byreference.

1-37. (canceled)
 38. A method of repairing a metallic alloy articlehaving a defect cavity greater than about 0.010 inches (2.54×10⁻⁴ m) inmaximum width, the method comprising the steps of: providing a firstmetallic filler material in the defect cavity such that the metallicfiller material substantially fills the cavity, the composition of thefirst metallic filler material corresponding substantially to that ofthe metallic alloy article; providing a second metallic filler materialover the first metallic filler material, wherein the second metallicfiller material includes between about 0 wt. % and about 40 wt. %metallic filler material of a composition corresponding substantially tothe metallic alloy article, and between about 100 wt. % and about 60 wt.% metallic filler material having the same basis as the composition ofthe metallic alloy article and including a melting point depressant inan amount substantially in excess of that in the metallic alloy article;effecting isothermal solidification by thermally processing the articlethrough a heat treatment comprising: heating the article to atemperature above the solidus of the second metallic filler material tomelt the second metallic filler material and isothermally solidifyrepair of the defect cavity greater than about 0.010 inches (2.54×10⁻⁴m) in maximum width.
 39. The method of claim 38 wherein the metallicalloy article is a nickel base superalloy article.
 40. The method ofclaim 38 wherein the defect cavity has a maximum width between about0.010 inches (2.5×10⁻⁴ m) and about 0.030 inches (7.6×10⁻⁴ m).
 41. Themethod of claim 38 wherein surface oxides are removed from the defectcavity prior to providing the first metallic filler material in thedefect cavity.
 42. The method of claim 38 wherein the metallic alloyarticle comprises a composition in weight percent of 9% chromium, 10%cobalt, 12.5% tungsten, 1% columbium, 2% titanium, 5% aluminum, 2%hafnium, 0.015% boron, balance nickel.
 43. The method of claim 38wherein between about 1% and 3%, boron, by weight, is present as themelting point depressant in the second metallic filler material.
 44. Themethod of claim 38 wherein the article is heated to between about 2000°F. (1093° C.) and about 2400° F. (1316° C.) for between about 5 hoursand about 30 hours, whereby the second metallic filler material meltsand infiltrates the first metallic filler material to produce a voidfree structure.
 45. A method of repairing a metallic alloy articlehaving a defect cavity, the method comprising the steps of: providing afirst metallic filler material in the defect cavity such that themetallic filler material substantially fills the cavity, the compositionof the first metallic filler material corresponding substantially tothat of the metallic alloy article; providing a second metallic fillermaterial over the first metallic filler material, wherein the secondmetallic filler material includes between about 0 wt. % and about 40 wt.% metallic filler material of a composition corresponding substantiallyto the metallic alloy article, and between about 100 wt. % and about 60wt. % metallic filler material having the same basis as the compositionof the metallic article and including a melting point depressant in anamount substantially in excess of that in the metallic alloy article;effecting isothermal solidification by thermally processing the articlethrough a heat treatment comprising: heating the article to atemperature (T1) capable of sintering the first metallic fillermaterial, but below the solidus of the second metallic filler material,such as between about 2000° F. (1093° C.) and about 2400° F. (1316° C.)for about 4 hours; and then holding at a temperature (T2) above thesolidus of the second metallic filler material, such as between about2000° F. (1093° C.) and about 2400° F. (131 6° C.) for between about 5hours and about 30 hours to melt the second metallic filler material andisothermally solidify the repair, whereby T2 is greater than T1.
 46. Amethod of repairing a metallic alloy article having a defect cavitygreater than about 0.010 inches (2.5×10⁻⁴ m) in maximum width, themethod comprising the steps of: providing a first metallic filler pastein the defect cavity such that the metallic filler paste substantiallyfills the cavity, the metallic filler paste comprising a binder and afirst metallic filler material having composition correspondingsubstantially to that of the metallic alloy article; providing a secondmetallic filler paste over the first metallic filler paste, wherein thesecond metallic filler paste comprises a binder and a second metallicfiller material having between about 0 wt. % and about 40 wt. % metallicfiller material of a composition corresponding substantially to themetallic article, and between about 100 wt. % and about 60 wt. %metallic filler material having the same basis as the composition of themetallic alloy article and including a melting point depressant in anamount substantially in excess of that in the metallic alloy article;effecting isothermal solidification by thermally processing the articlethrough a heat treatment by: heating the article to a temperaturebetween about 1000° F. (538° C.) and about 1200° F. (649° C.) andholding at that temperature until the binder is driven off; holding at atemperature capable of sintering the first metallic filler material ofthe first metallic filler paste, but below solidus of the secondmetallic filler paste, between about 1850° F. (1010° C.) and about 2200°F. (1204° C.) for about 4 hours; and holding at a third temperature,between about 2000° F. (1093° C.) and about 2400 ° F. (1316° C.) forbetween about 5 hours and about 30 hours, to melt the second metallicfiller paste and thereby isothermally solidify a repair of the defectcavity greater than about 0.010 inches (2.5×10⁻⁴ m) in maximum width.47. A method of repairing a metallic alloy article having a defectcavity, the method comprising the steps of: providing a first metallicfiller material in the defect cavity such that the metallic fillermaterial substantially fills the cavity, wherein the first metallicfiller material is a blend of at least two distinct metallic fillermaterials, one metallic filler material, present in at least 60 wt. %,corresponds substantially in composition to that of the metallic alloyarticle, and another metallic filler material has the same basis as themetallic alloy article and includes a melting point depressant in anamount substantially in excess of that in the article; providing asecond metallic filler material over the first metallic filler material,wherein the second metallic filler material includes between about 0 wt.% and about 40 wt. % metallic filler material of a compositioncorresponding substantially to the metallic alloy article, and betweenabout 100 wt. % and about 60 wt. % metallic filler material having thesame basis as the metallic alloy article and including a melting pointdepressant in an amount substantially in excess of that in the metallicalloy article; effecting isothermal solidification by thermallyprocessing the article through a heat treatment comprising: heating thearticle to a temperature above the solidus of the second metallic fillermaterial to melt the second metallic filler material and isothermallysolidify the repair.
 48. A method of repairing a metallic alloy articlehaving a defect cavity of from 0.030 inch to ⅛ inch in width, the methodcomprising the steps of: providing a first metallic filler material inthe defect cavity such that the first metallic filler materialsubstantially fills the cavity, the first metallic filler materialcomprising a first metallic filler and a first binder, the compositionof the first metallic filler corresponding substantially to thecomposition of the metallic alloy article, the first binder consistingessentially of 25-50% by weight of a first thermoplastic resin, 25-60%by weight of a first solvent for the first thermoplastic resin whichsubstantially vaporizes at temperatures up to 200° C., 0-30% by weightof a first plasticizer and 0-5% by weight of a first wetting agent; thefirst metallic filler material comprising 85-95% by weight of the firstmetallic filler and 5-15% by weight of the first binder; providing asecond metallic filler material over the first metallic filler material,wherein the second metallic filler material includes a second metallicfiller and a second binder, the second metallic filler comprising about100 wt. % of a metallic filler having the same basis as the compositionof the metallic alloy article and including a melting point depressantin an amount substantially in excess of any amount of melting pointdepressant in the metallic alloy article, the second binder consistingessentially of 25-50% by weight of a second thermoplastic resin, 25-60%by weight of a second solvent for the second thermoplastic resin whichsubstantially vaporizes at temperatures up to 200° C., 0-30% by weightof a second plasticizer and 0-5% by weight of a second wetting agent;the second metallic filler material comprising 85-95% by weight of thesecond metallic filler and 5-15% by weight of the second binder;effecting isothermal solidification by thermally processing the articlethrough a heat treatment comprising: heating the article to atemperature up to 200° C. to remove the solvents in the first and secondbinders so as to dry the article; heating the article to a temperaturesufficient to decompose remaining binder into gaseous products; heatingthe article to a temperature sufficient to evaporate the gaseousproducts; and heating the article to a temperature above the solidus ofthe second metallic filler material to melt the second metallic fillermaterial and isothermally solidify repair of the defect cavity.
 49. Themethod of claim 48 wherein the defect cavity has a width of about 0.030inches (7.6×10⁻⁴ m).
 50. The method of claim 48 wherein about 2.7% boronby weight is present as the melting point depressant in the secondmetallic filler material.
 51. The method of claim 48 wherein the articleis heated to between about 1176° C. and about 1204° C. for between about5½ hours and about 7 hours, whereby the second metallic filler melts andinfiltrates the first metallic filler material to produce a void freestructure.
 52. A method of repairing a metallic alloy article having adefect cavity of from about 0.010 inches to about ⅛ inch in width, themethod comprising the steps of: providing a first metallic fillermaterial in the defect cavity such that the first metallic fillermaterial substantially fills the cavity, the first metallic fillermaterial comprising a first binder and a first metallic filler, thefirst metallic filler having a composition corresponding substantiallyto the composition of the metallic alloy article; the first binderconsisting essentially of 25-50% by weight of a first thermoplasticresin, 25-60% by weight of a first solvent for the first thermoplasticresin which substantially vaporizes at temperatures up to 200° C., 0-30%by weight of a first plasticizer and 0-5% by weight of a first wettingagent; the first metallic filler material comprising 85-95% by weight ofthe first metallic filler and 5-15% by weight of the first binder;providing a second metallic filler material over the first metallicfiller material, wherein the second metallic filler material comprises asecond binder and a second metallic filler, the second metallic fillercomprising about 100 wt. % of a metallic filler having the same basis asthe composition of the metallic alloy article and including a meltingpoint depressant in an amount substantially in excess of any amount ofmelting point depressant in the metallic alloy article, the secondbinder consisting essentially of 25-50% by weight of a secondthermoplastic resin, 25-60% by weight of a second solvent for the secondthermoplastic resin which substantially vaporizes at temperatures up to200° C., 0-30% by weight of a second plasticizer and 0-5% by weight of asecond wetting agent; the second metallic filler material comprising85-95% by weight of the second metallic filler and 5-15% by weight ofthe second binder; effecting isothermal solidification by thermallyprocessing the article through a heat treatment comprising: heating thearticle to a temperature up to 200° C. to remove the solvents in thefirst and second binders so as to dry the article; heating the articleto a temperature sufficient to decompose remaining binder into gaseousproducts; heating the article to a temperature sufficient to evaporatethe gaseous products; and holding at a temperature capable of sinteringthe first metallic filler of the first metallic filler material, butbelow the solidus of the second metallic filler material; and holding ata third temperature sufficient to melt the second metallic fillermaterial and thereby isothermally solidify the repair of the defectcavity.